ARS | Publication request: The persistence of Gliocephalotrichum bulbilium and G. simplex causing fruit rot of rambutan in Puerto Rico

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: April 2, 2012
Publication Date: November 1, 2012
Citation: Serrato-Diaz, L., Rivera-Vargas, L., Latoni-Brailowsky, E., Goenaga, R.J. 2012. The persistence of Gliocephalotrichum bulbilium and G. simplex causing fruit rot of rambutan in Puerto Rico. Phytopathology. 102:S6.6.

Technical Abstract: Fruit rot of rambutan (Nephelium lappaceum L.) is a pre and post-harvest disease problem that affects fruit quality. Significant post-harvest losses have occurred worldwide and several pathogens have been identified in Malaysia, Costa Rica, Hawaii, Thailand, and Puerto Rico. In 2011, fruit rot was observed on rambutan at the USDA-ARS Tropical Agriculture Station in Mayaguez. Infected fruit sections (1mm2) were surface sterilized, rinsed with sterile deionized-distilled water and transferred to acidified potato dextrose agar (APDA). Isolates of Gliocephalotrichum spp. were recovered from diseased fruit tissue and diferentiated based on morphological characteristics such as color, texture of the colonies, and the production of reproductive structures. In 2008, this genus had also been observed on rambutan. Twentysix isolates were transferred to carnation leaf agar for morphological, molecular and pathogenicity characterization. Using light microscopy, scanning electron microscopy, and PCR amplification of the ITS1-5.8S-ITS2 region of the rDNA and ß-tubulin partial cds gene, 13 isolates were clearly divided into G. bulbilium (Gb) and 13 into G. simplex (Gs). Sequence analyses gave 100% identity with these two species. Morphologically, Gb was identified by the presence of bulbilloid aggregates and stipe extensions that were mostly located adjacent to the start of the conidiogenous penicilli. For Gs, conidiophores had stipe extensions rising at some distance away from the conidiogenous penicilli, with no bulbilloid aggregates but with chlamydospores that were unicellular, brown, smooth, and thick-walled. Pathogenicity tests were conducted on healthy superficially sterilized fruits. Fruits were inoculated with 5-mm mycelial disks of 8-day-old pure cultures grown in APDA. Untreated controls were inoculated with APDA disks only. Five days after inoculation (DAI), white mycelial growth for Gb and golden mycelia growth for Gs were observed on fruits. Eight DAI, fruit rot symptoms were observed on both isolates of Gb and Gs and conidiophores were observed on spintems (hair-like appendages).